The present invention relates to a method and a device for controlling the knock of an internal combustion engine.
In an internal combustion engine, the spontaneous ignition of the fresh mixture not yet reached by the flame front can result in the occurrence of abnormal combustion processes, which are referred to as engine knock. Due to the increased thermal stress and the pressure waves that occur, persistent engine knock can result in damage to the component parts of the combustion chamber.
The ignition firing point is an important parameter that influences the tendency of the internal combustion engine to experience knocking. Combustion knock occurs when the fuel-air mixture in the combustion chamber is ignited too soon. Therefore, a possible measure for eliminating engine knock after its detection, in subsequent combustion, is to retard the ignition firing point.
Overretarded ignition is associated with a loss of efficiency. Therefore, a knock control system, which initially determines if combustion knock has occurred, is used in internal combustion engines. This part of the knock control is known as knock detection. Secondly, the ignition-advance angle is adjusted during the knock control. An example of such knock control is known from the International Publication No. WO 91/14097. However, other regulated quantities, such as the fuel-air mixture, the charge, the compression ratio, and the operating point of the engine, can be changed in order to reduce the knock sensitivity of an engine.
It is also known, that the engine knock can be controlled in a cylinder-selective manner, i.e. both the knock detection and the adjustment of the ignition-advance angle are carried out separtely for each cylinder. Constructional differences in the cylinders and non-uniform distribution of the knock sensors and the accompanying cylinder-selective knock signals result in cylinder-specific differences in the knock control, so that a cylinder-selective knock control reduces the knock sensitivity, while simultaneously optimizing the efficiency.
If the phase detector, which supplies the signals forming the basis of the ignition synchronization and the knock-control synchronization, malfunctions, then the cylinder-selective knock control implemented up to this point is subject to new requirements. In this case, the knock control should function in a highly reliable manner because of possible damage to the engine, and should function with high accuracy to attain a maximum efficiency.
The method and device according to the present invention have the advantage, that the knock control can be designed to be variable, depending on the activation of dual ignition. Non-cylinder-specific measures influencing the knock control are carried outas an emergency strategy. Since this can change during the running time of the engine, or after restarting it, it is also advantageous that the method and device of the present invention adapt to the specific operating state of the engine. Thus, a maximum efficiency can be realized for the combustion, and a high degree of reliability can be attained for the knock control. For example, the method of the present invention allows the knock control to be optimized in spite of the phase detector malfunctioning, when the sychronization could be restored by another measure.
Further advantages resulting from the exemplary embodiments of the present invention relate to the special, non-cylinder-specific measures implemented there. These advantages offer a high degree of reliability in eliminating occurrances of knock, owing to the selection of the knock-detection threshold value or the selection of the ignition-advance angle.
The present invention can be further improved by integrating the method and device of the present invention, which include the various, non-cylinder-selective measures, into a universal control unit that selects a special, non-cylinder-selective measure as a function of the type of engine and the operating state. This multifunction control unit can be used for various types of engines; in each case, the multifunction control unit selecting the most suitable, non-cylinder-specific measure.